Nanoporous chelating fibers

ABSTRACT

A composite includes substrate fibers, and an organosilica coating including a structure-directing template, on the substrate fibers. The composite may be formed by coating substrate fibers with an organosilica sol containing a structure-directing template, and curing the organosilica sol to form an organosilica coating. A nanoporous chelating fiber includes a substrate fiber and a nanoporous chelating coating, on the substrate fiber. Nanoporous chelating fibers may be formed by removing the structure-directing template from a composite to form a nanoporous chelating coating on the substrate fibers. Contaminants may be removed from a fluid by contacting nanoporous chelating fibers with a fluid containing at least one contaminant.

REFERENCE To RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/544,847 entitled “Nanoporous Organic/Inorganic Hybrid ChelatingFibers” filed Feb. 13, 2004, which is incorporated by reference in itsentirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The subject matter of this application may have been funded in partunder a research grants from the Science and Technology Center (STC)program of the National Science Foundation (NSF), under Agreement NumberCTS-0120978. The U.S. Government may have rights in this invention.

BACKGROUND

The removal of contaminants from air, water and oil in industrial,commercial, or residential environments is a problem that is becomingmore serious in recent years, prompting the establishment ofincreasingly stringent government regulations demanding that levels ofcontaminants be lowered. In particular, the removal of contaminants suchas organic compounds, heavy metals, and radioactive metals from air,water, and oil is the focus of much research. The contamination ofgroundwater and, ultimately, drinking water is the driving force behindthe extensive research being conducted in order to remove toxic andhazardous contaminants from wastewater. The wastewater containscontaminants such as mercury, arsenic and iron, which react with oxygen;negatively charged metals such as arsenic, molybdenum, and chromium; andpositively charged heavy metals such as silver, lead, and nickel.Disposing of wastewater is not only very expensive and time consuming,but also extremely harmful to the environment. Current processes for theremoval of contaminants from air, water, and oil include incineration,adsorption, impingement, electrostatic attraction, centrifugation, sonicagglomeration, ozonization, membrane separation, ion exchange, andsolvent extraction. However, all of these processes have someimpediments for use in industrial applications. For example, there are anumber of drawbacks associated with the traditional approach to ionexchange bead synthesis. During functionalization of the polymericsystems, swelling agents must be used to reduce effects of osmotic shockand to maintain the spherical form of the bead. Furthermore,environmentally unfriendly solvents including toluene, methylenechloride, perchloethylene and carbon tetrachloride, etc. are used in thesynthesis and carry an added expense not only in their initial cost butalso in the EPA requirements for handling spent solvents.

Recently, hybrid mesoporous powder materials with functionalizedmonolayers containing thiol groups have been used as adsorbents toremove heavy metals from waste streams. See, for example, Feng et al.Science 276: 923-6 (1997); Liu et al. Chem. Eng. Tech. 21: 97-100(1998); Mercier et al. Environ. Sci. Tech. 32: 2749-54 (1998); and Liuet al. Adv. Mater. 10: 161 +(1998); and PCT Application Publication No.WO 98/34723, all of which are incorporated herein by reference. Thesefunctionalized hybrid materials show selectivity and high loadingcapacity for mercury (II) ions and many other heavy metals. Althoughthese functionalized hybrid materials show potential as heavy metaladsorbents, the requirements of mesoporosity, high ordering, and highsurface areas make the synthesis of these materials quite complex. Inaddition, the ligand loading capacity of these materials is limited bythe quantity and availability of anchoring residual silanol groups onthe pore surface. Furthermore, environmentally hazardous solvents, suchas toluene, were used in the functionalization process of the materials.

Glass fibers coated with ion-exchange polymers have been investigated asa low cost approach to contaminant removal. See, for example, Economy etal., Ind. Eng. Chem. Res. 41: 6436-42 (2002); Dominguez et al., Polym.Adv. Tech. 12: 197-05 (2001); and U.S. Pat. No. 6,706,361 B1, all ofwhich are expressly incorporated herein by reference. These polymericion exchange fibers have the potential to remove a wide range ofcontaminant ions from water such as mercury, cadmium, lead, and cyanideions. It would be desirable to improve certain properties of thesefibers, such as selectivity and efficiency in removal of toxic heavymetal ions and radioactive metal ions from air, water, and oil in thepresence of high concentrations of nontoxic competing ions such assodium and potassium.

Nonporous polymeric chelating fibers have been investigated forselective removal of trace levels of mercury and radioactive cesium ionsfrom water. See, for example, Liu et al., Environ. Sci. Tech., 37:4261-4268 (2003); Liu et al., C&E News, September 15: p21 (2003), eachof which is expressly incorporated herein by reference. It would bedesirable to improve certain properties of these fibers, such as theloading capacity and sorption kinetics for contaminants.

It would be desirable to provide more effective and efficient materialsand methods to remove contaminants, particularly toxic heavy metal ionsand radioactive metal ions from the air, water, and oil.

SUMMARY

In one aspect, the invention provides a nanoporous chelating fiber thatincludes a substrate fiber and a nanoporous chelating coating, on thesubstrate fiber.

In another aspect of the invention, there is a composite that includessubstrate fibers, and an organosilica coating that includes astructure-directing template, on the substrate fibers.

In yet another aspect of the invention, there is a method of forming acomposite that includes coating substrate fibers with an organosilicasol containing a structure-directing template, and curing theorganosilica sol to form an organosilica coating.

In yet another aspect of the invention, there is a method of formingnanoporous chelating fibers that includes removing thestructure-directing template from a composite to form a nanoporouschelating coating on the substrate fibers.

These aspects may include methods of forming composites and/ornanoporous chelating fibers wherein the organosilica sol is formed bycombining ingredients including an organotrialkoxysilane having achelating group, a tetraalkoxysilane, a structure-directing template, anacid catalyst, water, and a volatile solvent. The combining may includeforming a homogeneous monomer mixture including theorganotrialkoxysilane, the tetraalkoxysilane, the acid catalyst, water,and the volatile solvent; and adding the structure-directing template tothe homogeneous monomer mixture. The removing the structure-directingtemplate may include contacting the organosilica coating with a mixtureincluding acid and a volatile solvent. The organotrialkoxysilane mayinclude a compound having the structure of formula (I):R(CH₂)_(n)Si (OR⁵)₃  (1)wherein —R is the chelating group, n is an integer from 0 to 20, and —R⁵is a C1-C8 hydrocarbon group.

In yet another aspect of the invention, there is a method of removing acontaminant from a fluid that includes contacting a nanoporous chelatingfiber with a fluid containing at least one contaminant. The fluid mayinclude a substance selected from the group consisting of water, an oiland a gas; the at least one contaminant may include a substance selectedfrom the group consisting of an alkali metal compound, an alkali earthmetal compound, a transition metal compound, a group III-VIII compound,a lanthanide compound and an actinide compound; and the at least onecontaminant may include a substance selected from the group consistingof a copper compound, a chromium compound, a mercury compound, a leadcompound, a silver compound, a zinc compound and an arsenic compound.The method may further include regenerating the nanoporous chelatingfiber after the contacting, where the regenerating includes treating thenanoporous chelating fiber with an aqueous acid solution.

These aspects may include nanoporous chelating fibers, composites,methods of forming the nanoporous chelating fibers and/or composites,and methods of removing contaminants wherein the nanoporous chelatingcoating includes an organosilica having a plurality of chelating groups;wherein the plurality of chelating groups includes at least onechelating group selected from the group consisting of a thiol, analcohol, a primary amine, a secondary amine, an ammonium group, and acalix[n]arene; wherein the plurality of chelating groups includes thiolgroups; wherein the substrate fiber includes a material selected fromthe group consisting of glass, mineral, ceramic, metal, natural fiberand polymer; wherein the substrate fiber is present with a plurality ofsubstrate fibers in a form selected from the group consisting of papers,fabrics, felts and mats; and wherein the structure-directing templateincludes a member selected from the group consisting ofcetyltrimethylammonium bromide, cetyltrimethylammonium chloride,CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH, (EO)₂₀(PO)₇₀(EO)₂₀, (EO)₁₀₅(PO)₇₀(EO)₁₀₅,dibenzoyl-/-tartaric acid and a cyclodextrin.

The scope of the present invention is defined solely by the appendedclaims and is not affected by the statements within this summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description.

FIG. 1 is a flowchart illustrating schematically the preparation of anexample of nanoporous thiol-functionalized organosilica chelatingfibers.

FIG. 2 is a graph illustrating the FTIR spectra of (a) originalCrane-230 glass fiber substrate and (b) MP-silica-20%-NC fibers.

FIG. 3 is a graph illustrating solid-state ¹³C NMR spectrum ofMP-silica-10%-NC fibers.

FIG. 4 is a graph illustrating the nitrogen adsorption-desorptionisotherms of (a) MP-silica-10%-NC, (b) MP-silica-20%-NC, and (c)MP-silica-50%-NC fibers.

FIG. 5 is a graph illustrating the pore size distributions for (a)MP-silica-10%-NC, (b) MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers,

FIG. 6 is a TEM image of MP-silica-10%-NC material coated on the glassfiber substrate.

FIG. 7 is a SEM image of MP-silica-10%-NC fibers.

FIG. 8 is a graph illustrating the changes of mercury concentrations asa function of time in the sorption reaction of MP-silica-10%-NC andMP-silica-50%-NC fibers. Initial Hg concentration: 3.7 ppm, 10 mL ofsolution with 2250 ppm of sodium ions, 0.1 g of MP-silica-10%-NC orMP-silica-50%-NC fibers.

FIG. 9 is a flowchart illustrating schematically a regeneration study onan example of mercury-loaded MP-silica-10%-NC fibers.

DETAILED DESCRIPTION

Nanoporous chelating fibers include substrate fibers and a nanoporouschelating coating, on the substrate fibers. These nanoporous chelatingfibers may be formed from a composite that includes substrate fibers,and an organosilica coating containing a structure-directing template,on the fibers. This type of composite may be formed by coating substratefibers with an organosilica sol containing the structure-directingtemplate, and then curing the organosilica sol. The composite may thenbe converted into nanoporous chelating fibers by removing thestructure-directing template. Nanoporous chelating fibers may be used toremove contaminants from fluids such as water, oil, gases and mixturesthereof.

The term “nanoporous,” as used herein, means a substance containingpores having an average diameter of 100 nanometers (nm) or smaller.

The term “chelating,” as used herein, means a substance that binds ametal atom with two or more ligands. At the molecular level, a chelatinggroup is any chemical group that forms a ligand with a metal atom.

The term “organosilica,” as used herein, means a silica (SiO_(x))network containing organic chemical groups.

The term “nanoporous organosilica chelating coating,” as used herein,means an organosilica that contains organic chelating groups, thusallowing the material to chelate specific metal ions.

Nanoporous chelating fibers can exhibit advantages over conventionalmaterials for purification of fluids. For example, nanoporous chelatingfibers can provide for increased kinetic rates of reaction andregeneration, reduced fracture and breakage, and improved strength anddimensional stability relative to conventional ion exchange resins inthe form of beads. In another example, nanoporous chelating fibers candisplay improved selectivity for specific toxic metal ions in air,water, and oil in the presence of high concentrations of nontoxic metalions, as compared with polymeric ion exchange fibers. In yet anotherexample, nanoporous chelating fibers may be manufactured more easily andless expensively than hybrid mesoporous powder materials due to therelatively simple synthetic procedures, and can provide bettermechanical integrity and wear resistance. A wide variety of nanoporouschelating fibers with different organic chelating groups, which arecapable of chelating/adsorbing a number of different contaminant metalions from air, water, and oil, can be produced by using differentnanoporous chelating materials. In a specific example, nanoporousorganosilica chelating fibers may have desirable properties includinglow-cost, high surface areas, controlled pore sizes, high mechanical anddimensional stabilities, and reduced swelling, as well as ease offabrication into felts, papers, or fabrics for scaling-up andcommercialization.

Nanoporous chelating fibers include substrate fibers, and a nanoporouschelating coating, on the surface of the substrate fibers. The substratefibers may include any material that can tolerate the conditionsnecessary to form the insoluble nanoporous chelating coating. Examplesinclude natural fibers, e-glass fibers, HEPA filters, synthetic fibersused in clothing, polyesters, polyethylene, polyethylene terephthalate,nylon 6, nylon 66, polypropylene, KEVLAR™, liquid crystallinepolyesters, and syndiotactic polystyrene. Other examples include naturaland synthetic fibers, for example: glass fibers; mineral fibers such asasbestos and basalt; ceramic fibers such as TiO₂, SiC, and BN; metalfibers such as iron, nickel and platinum; polymer fibers such as TYVEK™;natural fibers such as cellulose and animal hair; and combinationsthereof. Some preferred substrate fibers are listed in Table 1.Preferably the fibers have a softening or decomposition temperature ofat most 350° C. TABLE 1 Commercially Available Substrate Fibers CompanyProduct Line Description CRANE & CO. Crane 230 (6.5 μm) Non-woven FiberGlass Mats Crane 232 (7.5 μm) Non-woven Fiber Glass Mats FIBER GLAST 519(0.75 oz.) Wovens 573 (9 oz.) Wovens HOLLINGSWORTH & BG05095 Glass Paperor Felts VOSE HE1021 JOHNS MANVILLE DURAGLASS ® 7529 Non-woven Fiber (11μm)) Glass Mats LYDALL MANNING MANNIGLAS ® Non-woven Fiber Glass MatsDUPONT TYVEK ® HDPE Spun Bonded Paper

The nanoporous chelating coating material may be any nanoporous materialthat contains chelating groups. Preferably the nanoporous material is ananoporous organosilica. Examples of nanoporous organosilica includematerials having the structure of formula (II):

in which —R is a chelating group, and n is an integer from 0 to 20. Thechelating group may be neutral or ionic, as long as the group forms aligand with a metal atom. A chelating coating may include a single typeof chelating group, or it may include more than one type of chelatinggroup. Examples of chelating groups include thiols (—SH); alcohols(—OH); amines, including primary amines (—NH₂) and secondary amines(—NR¹H); ammonium groups, including trialkyl ammonium groups(—[NR²R³R⁴]⁺); calix[n]arenes; and mixtures thereof, where R¹, R², R³and R⁴ may be alkyl or aryl groups. Specific examples of —R groupsinclude —SH, —OH, —NH₂, —NR¹H, —(CH₂)_(n)NH(CH₂)₂NH₂,—OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, calix[n]arenes (n=4, 6, or 8),—[NCH₃((CH₂)_(a)CH₃)₂]⁺ Cl⁻, —[N(CH₂)₁₇CH₃(CH₃)₂]⁺Cl⁻, —[N(CH₃)₃]⁺ Cl⁻,—[N(CH₂CH₃)₃]⁺ Cl⁻, and —[N(CH₂CH₂CH₂CH₃)₃]⁺ Cl⁻.

Nanoporous chelating fibers may be prepared by coating substrate fiberswith a template-directed organosilica sol to form an organosilicacoating on the surface of the substrate fibers. Curing of theorganosilica coating forms a composite having an insoluble organosilicacoating on the surface of the substrate fibers. Subsequent removal ofthe template from the insoluble organosilica coating produces nanoporouschelating fibers having an organosilica chelating coating.

A template-directed organosilica sol may be prepared by mixing anorganotrialkoxysilane, a tetraalkoxysilane, a structure-directingtemplate, an acid catalyst, water, and a volatile solvent. The ratio oforganotrialkoxysilane to tetraalkoxysilane in the template-directedorganosilica sol may be varied from 0:100 to 100:100. This sol containsan organosilica network organized around micelles of thestructure-directing template. The sol may be applied to the fibers by avariety of coating methods and then dried. Examples of coating methodsinclude dip-coating and spray coating. The coated fibers may be cured,for example at 100-150° C., to form an insoluble organosilica network onthe surface of the substrate fibers. Removal of the template results inthe formation of nanoporous organosilica chelating fibers.

Structure-directing templates may be ionic surfactants, neutralsurfactants, or non-surfactants. Examples of structure-directingtemplates include ionic surfactants, such as cetyltrimethylammoniumbromide (CTABr) and cetyltrimethylammonium chloride (CTACl); neutralsurfacants such as CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH (Brij-56; UNIQEMA, NewCastle, DE), (EO)₂₀(PO)₇₀(EO)₂₀ (Pluronic-P123, where EO is ethyleneoxide and PO is propylene oxide; BASF Corporation, Mount Olive, N.J.),(EO)₁₀₅(PO)₇₀(EO)₁₀₅ (Pluronic-F127, where EO is ethylene oxide and POis propylene oxide; BASF); non-surfactants such as dibenzoyl-/-tartaricacid and cyclodextrins; and derivatives and analogs thereof.

In one example, a method of forming the nanoporous chelating coating onthe surface of substrate fibers includes synthesizing an organosilicasol using a structure-directing template, and then applying the solutionto the substrate fibers. The template-directed organosilica sol may beprovided by first preparing a homogeneous organosilane monomer solutionby mixing organotrialkoxysilane monomer and tetraalkoxysilane monomer,water, an acid catalyst and a volatile solvent. The molar percentage(mol %) of organotrialkoxysilane monomer to the total amount of monomermay be from zero to 100, and preferably is from 5 to 40 mol %.Preferably the water is deionized water. In one example, a homogeneousorganosilane monomer solution contains a molar ratio oforganotrialkoxysilane to tetraalkoxysilane to volatile solvent todeionized water to acid catalyst of x:(1−x):1-10:0.5-5:1×10⁻⁵−10×10⁻⁵,where x is a number from zero to 1. Examples of acid catalysts includehydrochloric acid, phosphoric acid, sulfonic acid, acetic acid, andmixtures thereof. Examples of volatile solvents include alcohols such asethanol or methanol; ethers such as diethyl ether; ketones such asacetone; and mixtures thereof.

The organotrialkoxysilane monomer may be a compound having the structureof formula (I):R(CH₂)_(n)Si(OR⁵)₃  (1)in which —R is a chelating group, n is an integer from 0 to 20, and —R⁵is a C1-C8 hydrocarbon group. Examples of chelating groups includethiols (—SH); alcohols (—OH); amines, including primary amines (—NH₂)and secondary amines (—NR¹H); ammonium groups, including trialkylammonium groups (—[NR²R³R⁴]⁺); calix[n]arenes; and mixtures thereof,where R¹, R², R³ and R⁴ may be alkyl or aryl groups. Specific examplesof —R groups include —SH, —OH, —NH₂, —NR¹H, —(CH₂)_(n)NH(CH₂)₂NH₂,—OCH₂CH(OH)CH₂N(CH₂CH₂OH)₂, calix[n]arenes (n=4, 6, or 8),—[NCH₃((CH₂)₉CH₃)₂]⁺ Cl⁻, [N(CH₂)₁₇CH₃(CH₃)₂]⁺ Cl⁻, —[N(CH₃)₃]⁺ Cl⁻,—[N(CH₂CH₃)₃]⁺Cl⁻, and —[N(CH₂CH₂CH₂CH₃)₃]⁺ Cl⁻.

The tetraalkoxysilane monomer may be a compound having the structure offormula (III):SI(OR⁶)₄  (III)in which —R⁶ is a C1-C8 hydrocarbon group.

A structure-directing template-may then be added to this homogeneousorganosilane monomer solution. The structure-directing template may beadded directly to the homogeneous organosilane monomer solution, or itmay be combined with other substances to form a template solution, whichmay then be added to the monomer solution. A template solution maycontain a mixture of the structure-directing template in a liquid suchas water and/or a volatile solvent, and may contain an acid catalyst.Examples of volatile solvents include alcohols such as ethanol ormethanol; ethers such as diethyl ether; ketones such as acetone; andmixtures thereof. Examples of acid catalysts include hydrochloric acid,phosphoric acid, sulfonic acid, acetic acid, and mixtures thereof. Inone example, a template solution contains a molar ratio of volatilesolvent to deionized water to acid catalyst to structure-directingtemplate of 1-20:0.5-5:0.001-0.005:0.1-0.3.

In a specific example of preparing an organosilica sol using astructure-directing template, a homogeneous organosilane monomersolution in deionized water may be refluxed at for example 60° C. for0.5-5 hours and then cooled to room temperature to provide apre-hydrolyzed sol solution. To this pre-hydrolyzed sol is added atemplate solution containing deionized water, an acid catalyst, astructure-directing template, and a volatile solvent. The solution isaged for 1-14 days to allow for the silica network to adequatelyorganize around the template micelles to produce the finaltemplate-directed organosilica sol used for coating the substratefibers.

The coated fibers may be exposed to air to dry the organosilica coating.The dried organosilica coating may then be cured in air or in vacuo byheating to form an insoluble organosilica chelating coating on thefibers. The structure-directing templates in the insoluble organosilicachelating coating can be removed from this composite by gently stirringthe coated fibers in a solution of acid.

In one example, the structure-directing templates are removed from acomposite by stirring the coated fibers in a mixture of 36 weightpercent (wt %) aqueous HCl and a volatile solvent, such that the weightratio of the fiber to HCl to volatile solvent is 1: 1-1.5:150-200. Thefibers may be stirred in this mixture at elevated temperature, such as50° C., for about 2 hours. The coated fibers are then washed repeatedlywith the volatile solvent, and dried in air or in vacuo by heating, forexample to about 120° C., to form nanoporous chelating fibers.

The nanoporous chelating fibers may be present in any form. Examplesinclude loose fibers, woven and non-woven fabrics, papers, felts andmats. The nanoporous chelating fibers may be made from substrate fibersalready present in a specific form, or the nanoporous chelating fibersmay first be prepared from loose substrate fibers, and made into thespecific form. The nanoporous chelating coating may be used as anadhesive to hold the fibers together. The length of the nanoporouschelating fibers is not limited, and may be, for example, 0.01 mm to 100m in length. The nanoporous chelating fibers may be prepared from longersubstrate fibers, then cut or chopped. The diameter of the nanoporouschelating fibers is also not limited, and may be, for example 100 Å to 1mm in diameter. Preferably, the fibers have an aspect ratio of at least10.

The nanoporous chelating coating on the nanoporous chelating fibers maybe present on isolated regions on the surface of the substrate fibers,may completely enclose the substrate fibers, or enclose all of thesubstrate fibers except the ends of the substrate fibers. For example,if the substrate fibers were completely enclosed by the nanoporouschelating coating, then chopping would result in the ends of the fibersbeing exposed.

The weight ratio between the nanoporous chelating coating and thesubstrate fibers is not limited, but may affect the final properties ofthe nanoporous chelating fibers. For example, if the amount of thenanoporous chelating coating is very large compared to the amount ofsubstrate fibers, the brittleness of the coating may reduce theflexibility of the nanoporous chelating fibers. Preferably, thenanoporous chelating fibers include 10 to 90% by weight of thenanoporous chelating coating, more preferably 20 to 80% by weight of thenanoporous chelating coating, including 30%, 40%, 50%, 60%, and 70% byweight of the nanoporous chelating coating.

Nanoporous chelating fibers may be used to remove contaminants fromfluids such as water, oil, gases and mixtures thereof. In thisapplication, nanoporous chelating fibers can display selectivity forspecific toxic metal ions in air, water, and oil in the presence of highconcentrations of nontoxic metal ions. For example, nanoporous chelatingfibers can exhibit high loading capacities for metal ions, highselectivities for specific metal ions in the presence of highconcentrations of competing ions, and quite rapid sorption kinetics fortoxic metal ions such as mercury, silver, lead, etc.

Contaminants that can be removed include alkali metal compounds, alkaliearth metal compounds, transition metal compounds, group III-VIIIcompounds, lanthanide compounds, and actinide compounds. Specificexamples of contaminants that can be removed include copper compounds,chromium compounds, mercury compounds, lead compounds, silver compounds,zinc compounds, and arsenic compounds. The fluids from whichcontaminants may be removed include liquids, such as water, oil andmixtures thereof, and includes gases, such as air.

In one example, nanoporous organosilica chelating fibers having thiolchelating groups shows a loading capacity for mercury ions up to 269 mgHg/g of coating. These fibers also show high selectivities for mercuryions, with a measured K_(d) for Hg greater than 637800 mL/g, as well asrapid sorption kinetics for mercury ions, removing >99 % of Hg within 30min at a solution-to-solid ratio of 100 mL/g.

Once nanoporous chelating fibers have been used to remove contaminantsfrom fluids, the chelating properties can be regenerated, allowing thefibers to be used again for removal of contaminants from a fluid. Forexample, nanoporous chelating fibers that have been loaded with metalions can be treated with an aqueous acid solution, and this treatmentmay result in 100% regeneration of the chelation capacity of the fibers.

In a specific example, a method of regenerating the contaminant-loadednanoporous chelating fibers includes soaking the contaminant-loadednanoporous chelating fibers in an 1.0-12.1 molar (M) aqueous acidsolution for 2-12 hours. The leached fibers may be rinsed repeatedlywith deionized water and dried in air or in vacuo to result in 100%regeneration of the nanoporous chelating fibers. Examples of acids thatmay be used for regeneration include hydrochloric acid, phosphoric acid,sulfonic acid, acetic acid, and mixtures thereof.

The following examples are provided to illustrate one or more preferredembodiments of the invention. Numerous variations can be made to thefollowing examples that lie within the scope of the invention.

EXAMPLES Example 1 Synthesis of Organosilica Chelating Fibers with CTABrTemplates

Thiol-functionalized organosilica sol solutions were prepared by amicellar templating technique. A typical synthetic procedure required amolar ratio of 1Si:20EtOH:5H₂O:0.004 HCl:0.14CTABr. Tetraethoxysilane(TEOS) and mercaptopropyltrimethoxysilane (MPTMS) were used as the Sisources. Sol solutions were prepared with MPTMS to the total amount ofSi molar ratios of x/100 (MP-silica-x %-CTABr sol solution, x=0-100). Amixture of MPTMS and TEOS corresponding to the appropriate molefraction, with a total of 72 mmol Si (for example, 1.4 g (7.2 mmol) ofMPTMS and 13.5 g (64.8 mmol) of TEOS for MP-silica-1 0%-CTABr solsolution), was mixed with a solution containing 1.3 g (72 mmol) of Dlwater, 0.13 mg of HCI and 9.9 g (216 mmol) of ethanol. The homogeneoussolution was refluxed at 60° C. for 1 h and then cooled to roomtemperature to result in a pre-hydrolyzed sol solution. Then a solutionconsisting of 5.18 g (288 mmol) of Dl water, 10.4 mg of HCl, 3.67 g(10.1 mmol) of CTABr, and 56.3 g (1.22 mol) of ethanol was added to thepre-hydrolyzed sol solution. The solution was aged for 7 days to allowfor the silica network to adequately organize around the CTABr micelles.The final homogeneous sol solution was then used as the dippingsolution.

Crane-230 glass fibers were dip-coated with a MP-silica-x %-CTABr solsolution for 10 min, and placed on a fine mesh screen. The coated glassfibers were dried in a hood at room temperature for 12 h. The driedfibers were cured at 120° C. for 48 h in an oven. The cured MP-silica-x%-CTABr fibers were allowed to cool to room temperature slowly andweighed immediately.

The extraction of CTABr surfactant templates was performed by gentlystirring a mixture of 1.0 g of MP-silica-x %-CTABr fibers in a solutionof 1.0 g of hydrochloric acid (36 wt. %) and 180 g of methanol in a 60°C. water bath for 4 h. The surfactant-extracted MP-silica-x %-NC fiberswere washed repeatedly with methanol, and dried for 24 h at 80° C. invacuo.

This synthetic procedure is illustrated schematically in FIG. 1. FIG. 1also applies in general to the synthetic procedures of Examples 2-4.

Example 2 Synthesis of Organosilica Chelating Fibers with Brij-56Templates

Thiol-functionalized organosilica sol solutions were prepared by amicellar templating technique. A typical synthetic procedure required amolar ratio of 1Si:20EtOH:5H₂O:0.004 HCl:0.14 CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH(Brij-56). Tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane(MPTMS) were used as the Si sources. Sol solutions were prepared withMPTMS to the total amount of Si molar ratios of x/100 (MP-silica-x%-Brij sol solution, x=0-100). A mixture of MPTMS and TEOS correspondingto the appropriate mole fraction, with a total of 72 mmol Si (forexample, 1.4 g (7.2 mmol) of MPTMS and 13.5 g (64.8 mmol) of TEOS forMP-silica-10%-Brij sol solution), was mixed with a solution containing1.3 g (72 mmol) of Dl water, 0.13 mg of HCI and 9.9 g (216 mmol) ofethanol. The homogeneous solution was refluxed at 60° C. for 1 h andthen cooled to room temperature to result in a pre-hydrolyzed solsolution. Then a solution consisting of 5.18 g (288 mmol) of Dl water,10.4 mg of HCl, 6.89 g (10.1 mmol) of Brij-56, and 56.3 g (1.22 mol) ofethanol was added to the pre-hydrolyzed sol solution. The solution wasaged for 7 days to allow for the silica network to adequately organizearound the Brij-56 micelles. The final homogeneous sol solution was thenused as the dipping solution.

Crane-230 glass fibers were dip-coated with a MP-silica-x %-Brij solsolution for 10 min, and placed on a fine mesh screen. The coated glassfibers were dried in a hood at room temperature for 12 h. The driedfibers were cured at 120° C. for 48 h in an oven. The cured MP-silica-x%-Brij fibers were allowed to cool to room temperature slowly andweighed immediately.

The extraction of Brij-56 templates was performed by gently stirring amixture of 1.0 g of MP-silica-x %-Brij fibers in a solution of 1.0 g ofhydrochloric acid (36 wt. %) and 180 g of methanol in a 60° C. waterbath for 4 h. The template-extracted MP-silica-x %-NB fibers were washedrepeatedly with methanol, and dried for 24 h at 80° C. in vacuo.

Example 3 Synthesis of Organosilica Chelating Fibers with Pluronic-P123Templates

The thiol-functionalized organosilica sol solutions were prepared by amicellar templating technique. A typical synthetic procedure required amolar ratio of 1Si:20EtOH:5H₂O:0.004HCl:0.14(EO)₂₀(PO)₇₀(EO)₂₀(Pluronic-P123, where EO is ethylene oxide and PO is propylene oxide).Tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS) wereused as the Si sources. Sol solutions were prepared with MPTMS to thetotal amount of Si molar ratios of x/100 (MP-silica-x %-P123 solsolution, x=0-100). A mixture of MPTMS and TEOS corresponding to theappropriate mole fraction, with a total of 72 mmol Si (for example, 1.4g (7.2 mmol) of MPTMS and 13.5 g (64.8 mmol) of TEOS forMP-silica-10%-P123 sol solution), was mixed with a solution containing1.3 g (72 mmol) of Dl water, 0.13 mg of HCl and 9.9 g (216 mmol) ofethanol. The homogeneous solution was refluxed at 60° C. for 1 h andthen cooled to room temperature to result in a pre-hydrolyzed solsolution. Then a solution consisting of 5.18 g (288 mmol) of Dl water,10.4 mg of HCl, 10.1 mmol of Pluronic-P123, and 56.3 g (1.22 mol) ofethanol was added to the pre-hydrolyzed sol solution. The solution wasaged for 7 days to allow for the silica network to adequately organizearound the Pluronic-P123 micelles. The final homogeneous sol solutionwas then used as the dipping solution.

Crane-230 glass fibers were dip-coated with a MP-silica-x %-P123 solsolution for 10 min, and placed on a fine mesh screen. The coated glassfibers were dried in a hood at room temperature for 12 h. The driedfibers were cured at 120° C. for 48 h in an oven. The cured MP-silica-x%-P123 fibers were allowed to cool to room temperature slowly andweighed immediately.

The extraction of Pluronic-P123 templates was performed by gentlystirring a mixture of 1.0 g of MP-silica-x %-P1 23 fibers in a solutionof 1.0 g of hydrochloric acid (36 wt. %) and 180 g of methanol in a 60°C. water bath for 4 h. The template-extracted MP-silica-x %-NP fiberswere washed repeatedly with methanol, and dried for 24 h at 80° C. invacuo.

Example 4 Synthesis of Organosilica Chelating Fibers with Pluronic-F127Templates

Thiol-functionalized organosilica sol solutions were prepared by amicellar templating technique. A typical synthetic procedure required amolar ratio of 1Si:20EtOH:5H₂O:0.004HCl:0.14(EO)₁₀₅(PO)₇₀(EO)₁₀₅(Pluronic-F127, where EO is ethylene oxide and PO is propylene oxide).Tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS) wereused as the Si sources. Sol solutions were prepared with MPTMS to thetotal amount of Si molar ratios of x/100 (MP-silica-x %-F127 solsolution, x=0-100). A mixture of MPTMS and TEOS corresponding to theappropriate mole fraction, with a total of 72 mmol Si (for example, 1.4g (7.2 mmol) of MPTMS and 13.5 g (64.8 mmol) of TEOS forMP-silica-10%-F127 sol solution), was mixed with a solution containing1.3 g (72 mmol) of Dl water, 0.13 mg of HCl and 9.9 g (216 mmol) ofethanol. The homogeneous solution was refluxed at 60° C. for 1 h andthen cooled to room temperature to result in a pre-hydrolyzed solsolution. Then a solution consisting of 5.18 g (288 mmol) of Dl water,10.4 mg of HCl, 10.1 mmol of Pluronic-F127, and 56.3 g (1.22 mol) ofethanol was added to the pre-hydrolyzed sol solution. The solution wasaged for 7 days to allow for the silica network to adequately organizearound the pluronic-F127 micelles. The final homogeneous sol solutionwas then used as the dipping solution.

Crane-230 glass fibers were dip-coated with a MP-silica-x %-F127 solsolution for 10 min, and placed on a fine mesh screen. The coated glassfibers were dried in a hood at room temperature for 12 h. The driedfibers were cured at 120° C. for 48 h in an oven. The cured MP-silica-x%-F127 fibers were allowed to cool to room temperature slowly andweighed immediately.

The extraction of Pluronic-F127 templates was performed by gentlystirring a mixture of 1.0 g of MP-silica-x %-F127 fibers in a solutionof 1.0 g of hydrochloric acid (36 wt. %) and 180 g of methanol in a 60°C. water bath for 4 h. The template-extracted MP-silica-x %-NF fiberswere washed repeatedly with methanol, and dried for 24 h at 80° C. invacuo.

Example 5 Analysis of Organosilica Chelating MP-silica-x %-CTABr Fibers

The chemical and physical properties of the nanoporous organosilicachelating fibers of Example 1 were characterized by a variety ofmethods. Table 2 lists some of these properties of the MP-silica-x %-NCfibers.

The chemical structures of the fibers were characterized by infraredspectroscopy (IR) and solid-state ¹³C and ²⁹Si nuclear magneticresonance (NMR). FTIR spectra of the nanoporous organosilica chelatingfibers were obtained on KBr pellets using a Nicolet Magna IR TMspectrophotometer 550. High-resolution ¹³C solid-state NMR spectra wererun at 75.5 MHz on a Varian VXR300 spectrometer with a ZrO₂ rotor andtwo aurum caps. The spinning speed was 6 kHz. FIG. 2 shows the FTIRspectra of (a) original Crane-230 glass fiber substrate and (b)MP-silica-20%-NC fibers. FIG. 3 shows the solid-state ¹³C NMR spectrumof MP-silica-10%-NC fibers. The results not only indicated that theorganosilica chelating materials were successfully coated on thesubstrate fibers, but also proved that the organic chelating groups werecovalently bound to silica.

The surface areas of all the fibers were determined by N₂ adsorption at77 K using an Autosorb-1 volumetric sorption analyzer controlled byAutosorb-1 for windows 1.19 software (Quantachrome). All samples wereoutgassed at 80° C. until the test of outgas pressure rise was passed by10 μHg/min prior to their analysis. FIG. 4 illustrates the nitrogenadsorption-desorption isotherms of (a) MP-silica-10%-NC, (b)MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers. FIG. 5 illustratesthe pore size distributions for (a) MP-silica-10%-NC, (b)MP-silica-20%-NC, and (c) MP-silica-50%-NC fibers. Nitrogenadsorption-desorption measurements on the nanoporous organosilicachelating fibers showed that the nanoporous organosilica chelatingfibers had high surface areas with average pore diameters of <20 nm.

TEM images were recorded on a Hitachi HF-2000 transmission electronmicroscope. FIG. 6 shows the TEM image of MP-silica-10%-NC materialcoated on the glass fiber substrate. Transmission electron microscopy(TEM) images of the nanoporous organosilica chelating fibers showed thatthe nanoporous organosilica chelating fibers had many nanopores withoutordered arrays.

SEM images were acquired using a Hitachi S4700 scanning electronmicroscope with an acceleration voltage of 5 kV. FIG. 7 illustrates theSEM image of MP-silica-10%-NC fibers. Scanning electron microscopy (SEM)images of the nanoporous organosilica chelating fibers showed thatalthough some bridging exists, most of the nanoporous organosilicachelating material was coated on the surface of the fibers rather thanoccurring randomly within all the void volumes between the fibers. Theremaining void volume and the nanoporous organosilica chelating coatingwould work together to facilitate the diffusion and access ofcontaminants to the chelating groups.

Mercury was determined in adsorption isotherm solutions with a PSAnalytical Cold Vapor Atomic Fluorescence Spectrometer.

Thermogravimetric (TGA) measurements were performed on a Hi-Res TAInstruments 2950 Thermogravimetric Analyzer. TGA analysis revealed thatthe nanoporous organosilica chelating fibers were thermally stable up to200° C. TABLE 2 Physicochemical characteristics of MP-silica-x %-NCfibers. Silica coating BET surface area Pore Hg²⁺ loading capacitycontent m²g⁻¹ of m²g⁻¹ of diameter mgg⁻¹ of mgg⁻¹ of Material (wt. %)material coating (nm) material coating MP-silica- 36.6 245 669 1.84 — —0%-NC MP-silica- 44.2 275 622 1.75 70.8 160.2 10%-NC MP-silica- 39.5 183463 1.49 90.0 228.0 20%-NC MP-silica- 44.8 0 0 — — — 50%-NC

Example 6 Equilibration Adsorption Isotherm Experiments of MP-silica-x%-NC Fibers with Mercury Solutions

Tenth gram samples of MP-silica-x %-NC fibers from Example 1 wereequilibrated with 10 mL solutions containing various concentrations ofmercury at room temperature. After the mixtures were shaken for 2 h,they were filtered through a 0.22 μm Nylon 66 filter and analyzed byatomic fluorescence for residual metal content. A Thermo ElementalExCell Inductively Coupled Plasma Mass Spectrometer (ICP-MS) was used todetermine solution concentrations of sodium and other toxic metal ionssuch as silver, lead, cesium, etc. Mercury was determined in adsorptionisotherm solutions with a PS Analytical Cold Vapor Atomic FluorescenceSpectrometer. Table 3 lists the analyzed concentrations of metal ions inaqueous solutions of mercury after treatment with MP-silica-x %-NCfibers. TABLE 3 Analyzed concentrations of metal ions in aqueoussolutions of mercury after treatment with MP-silica-x %-NC fibers. Ionconcentrations after treatment (ppm) Solution 1* Solution 2** MaterialHg Hg Na K_(d) of Hg (mLg⁻¹) MP-silica-0%-NC 2.5 3.4 2170 —MP-silica-10%-NC 0.00037 0.00058 2100 637 800 MP-silica-20%-NC 0.00050.0012 2140 308 233 MP-silica-50%-NC 0.0081 0.0092 2150  40 117*Initial concentration of Hg in solution 1 is 2.5 ppm.**Initial concentrations of Hg and Na in solution 2 are 3.7 ppm and 2170ppm, respectively.

Example 7 Mercury Sorption Kinetics for MP-silica-x %-NC Fibers

Kinetic experiments were conducted for MP-silica-x %-NC fibers fromExample 1 in the same fashion as the adsorption isotherm experiments,except that the mixtures were shaken for 1 min, 3 min, 5 min, 10 min, 30min, 60 min and 120 min, respectively, and then filtered through a 0.22μm Nylon 66 filter and analyzed by atomic fluorescence for residualmetal content. FIG. 8 shows the changes of mercury concentrations as afunction of time in the sorption reaction of MP-silica-10%-NC andMP-silica-50%-NC fibers.

Example 8 Regeneration Studies on Mercury-Loaded MP-silica-x %-NC Fibers

MP-silica-x %-NC fibers from Example 1 that had been loaded with mercurywere soaked in an aqueous HCl solution (5.0 M) for 6 h. The mixture wasfiltered and the mercury concentration in the filtrate was determined byAtomic Fluorescence Spectrometry. The leached fibers were rinsedrepeatedly with Dl water and oven dried at 60° C. overnight prior toreuse. Tenth gram samples of leached MP-silica-x %-NC fibers wereallowed to equilibrate in 10 mL solutions of 3.7 ppm mercury and 2170ppm sodium for 2 h with shaking at room temperature. The solution wasfiltered through a 0.22 μm Nylon 66 filter and analyzed for mercury byAtomic Fluorescence Spectrometry and for sodium by ICP-MS. FIG. 9schematically illustrates the regeneration study on the mercury-loadedMP-silica-10%-NC fibers.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that other embodimentsand implementations are possible within the scope of the invention.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents.

1. A nanoporous chelating fiber, comprising: a substrate fiber; and ananoporous chelating coating, on the substrate fiber.
 2. The nanoporouschelating fiber of claim 1, wherein the nanoporous chelating coatingcomprises an organosilica comprising a plurality of chelating groups. 3.The nanoporous chelating fiber of claim 2, wherein the plurality ofchelating groups comprises at least one chelating group selected fromthe group consisting of a thiol, an alcohol, a primary amine, asecondary amine, an ammonium group, and a calix[n]arene.
 4. Thenanoporous chelating fiber of claim 2, wherein the plurality ofchelating groups comprises thiol groups.
 5. The nanoporous chelatingfiber of claim 1, wherein the substrate fiber comprises a materialselected from the group consisting of glass, mineral, ceramic, metal,natural fiber and polymer.
 6. The nanoporous chelating fiber of claim 1,wherein the substrate fiber is present with a plurality of substratefibers in a form selected from the group consisting of papers, fabrics,felts and mats.
 7. A composite, comprising: substrate fibers; and anorganosilica coating comprising a structure-directing template, on thesubstrate fibers.
 8. The composite of claim 7, wherein thestructure-directing template comprises a member selected from the groupconsisting of cetyltrimethylammonium bromide, cetyltrimethylammoniumchloride, CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH, (EO)₂₀(PO)₇₀(EO)₂₀,(EO)₁₀₅(PO)₇₀(EO)₁₀₅, dibenzoyl-/-tartaric acid and a cyclodextrin. 9.The composite of claim 7, wherein the organosilica coating furthercomprises a plurality of chelating groups.
 10. The composite of claim 9,wherein the plurality of chelating groups comprises at least onechelating group selected from the group consisting of a thiol, analcohol, a primary amine, a secondary amine, an ammonium group, and acalix[n]arene.
 11. A method of forming a composite, comprising: coatingsubstrate fibers with an organosilica sol comprising astructure-directing template; and curing the organosilica sol to form anorganosilica coating.
 12. The method of claim 11, wherein theorganosilica sol is formed by combining ingredients comprising anorganotrialkoxysilane comprising a chelating group, a tetraalkoxysilane,a structure-directing template, an acid catalyst, water, and a volatilesolvent.
 13. The method of claim 12, wherein the combining comprises:forming a homogeneous monomer mixture comprising theorganotrialkoxysilane, the tetraalkoxysilane, the acid catalyst, water,and the volatile solvent; and adding the structure-directing template tothe homogeneous monomer mixture.
 14. The method of claim 12, wherein theorganotrialkoxysilane comprises a compound having the structure offormula (I):R(CH₂)_(n)Si(OR⁵)₃  (I)wherein —R is the chelating group, n is aninteger from 0 to 20, and —R⁵ is a C1-C8 hydrocarbon group.
 15. Themethod of claim 12, wherein the chelating group is selected from thegroup consisting of a thiol, an alcohol, a primary amine, a secondaryamine, an ammonium group, and a calix[n]arene.
 16. The method of claim12, wherein the chelating group is a thiol.
 17. The method of claim 11,wherein the structure-directing template comprises a member selectedfrom the group consisting of cetyltrimethylammonium bromide,cetyltrimethylammonium chloride, CH₃(CH₂)₁₅(OCH₂CH₂)₁₀OH,(EO)₂₀(PO)₇₀(EO)₂₀, (EO)₁₀₅(PO)₇₀(EO)₁₀₅, dibenzoyl-/-tartaric acid anda cyclodextrin.
 18. A method of forming nanoporous chelating fibers,comprising: removing the structure-directing template from the compositeof claim 7 to form a nanoporous chelating coating on the substratefibers.
 19. The method of claim 18, wherein the removing thestructure-directing template comprises contacting the organosilicacoating with a mixture comprising an acid and a volatile solvent.
 20. Amethod of removing a contaminant from a fluid, comprising: contactingthe nanoporous chelating fiber of claim 1 with a fluid comprising atleast one contaminant.